This invention relates in general to computer software and more specifically to a system for preventing accurate disassembly of computer programs.
Computer software manufacturers have a keen interest in protecting their software. Software can be easily copied, in whole or in part, by making digital copies. Other forms of the copying do not require a competitor to copy the actual digital data, but are based on a knowledgeable programmer viewing the instructions within the software to gain information that can allow the programmer to “break” security systems, obtain valuable programming techniques or trade secrets of the software manufacturer, make derivations, manipulate the operation of the original code, etc.
One barrier to copying computer software is that many forms of software are distributed in a format that is not easily decipherable, or readable, by a human.
FIG. 1B is an illustration of various forms in the prior art which a computer program, or software, is transformed into during the process of creation, distribution, and ultimate execution of the software on a user's machine.
In FIG. 1B, human readable source code 10 is developed by a programmer who is the original author, and owner, of the work. Such source code is easily readable and understandable by a human programmer since the source code is written in text that resembles plain English with mathematical and logical equations. Many different forms of source code exist today based on many different types of computer languages. “Assembly code” is a form of human-readable code that is closely tied to a specific microprocessor's instruction set. Assembly code has many similarities to source code in terms of the form translations that the assembly code undergoes prior to being executed. For purposes of this specification, source code and assembly code can be treated similarly, and terminology and concepts associated with source code and assembly code can be interchanged. For example, as discussed below, compilation and assembly are analogous, as are decompilation and disassembly.
Returning to FIG. 1B, source code 10 is compiled by compiler 12. Compiler 12 is a software process that translates human-readable source code to a series of numbers which is, for the most part, unreadable by humans. Source code 10 is thus transformed, or “compiled,” by compiler 12 to form the human-unreadable object code. Object code 14 can be linked by linker 20 with other object code modules as illustrated by object code modules 16 and 18 in FIG. 1B. Once the object code modules are linked by linker 20, they form executable program 22. Executable program 22 can be loaded by loader 24 into a user's computer to form executing image 26. Executing image 26 represents the actual numerical information that is executed by a microprocessor within an end-user's computer.
Note that all forms of source code 10 that exists after compilation by compiler 12 are, for the most part, unreadable by a human. In other words, object code modules 14, 16 and 18; executable program 22; and executing image 26 are basically unformatted conglomerations of numbers that are extremely difficult to understand.
However, tools exist to decompile, or disassemble, these unreadable versions of source code. Decompiler 28 can accept the unformatted numbers of object code 14, executable program 22 or executing image 26 and produce a readable version of the original source code program. Such a readable version is referred to as decompiled (or disassembled) code 30. While the decompiled code is usually not as readable as original source code 10, it is a very effective tool for allowing an experienced programmer to understand the operation of the computer program and greatly reduces the amount of time required to copy, hack, or otherwise manipulate source code produced by an original programmer.
Thus, it is desirable to produce an invention which prevents, or reduces the effectiveness of decompilation, or disassembly, of compiled or assembled code.